Sodium

Na+ 135-145 meg/L

  • H2O – 60% male, 50% female
  • TBW – 1/3 ECF (1/4 IV, ¾ IS) , 2/3 ICF
  • 85-90% of total body Na+ is extracellular (95% K+ is intracellular)

ECF Volume

  • Depletion: deficit in total body Na+ (renal or extrarenal loss > Na intake)
  • Expansion: salt intake with renal Na+ retention (renal disorder or 2O to decrease effective circulating volume – HF or hypoalbumin)

Hyponatremia

  • Isotonic → hyperlipidemia, hyperprotenemia; no change in osmolarity; ↓ H2O volume so that ↓[Na] in plasma volume (pseudo!)
  • Hypertonic → hyperglycemia; ↑ glucose draws H2O into EC space from cells
  • Hypotonic → assess volume status (clinically)
    • Hypovolemic:
      • Extrarenal salt loss (GI)
      • Renal salt loss (diuretics, ACEi, mineralocorticoid deficiency, etc.)
    • Euvolemic:
      • SIADH (↓Na, ↓urea, ↓plasma osmolarity, ↑urine osmolarity)
      • Psychogenic polydipsia
      • Asymptomatic
        • H2O restric
        • 0.9% NS and furosemid
        • Demeclocycline – inhibit AD
      • Symptomatic
        • Saline 3% and furosemid
      • Watch out for central pontine myelinolysis if corrected too fast (1-2 meq/L/h
    • Hypervolemic: edema associated disease
      • Treatment – H2O restrict and diuretics



 

Hypernatremia

  • Concentrated urine (urine osmolarity > 400 mosm/kg)
      • renal H2O conserving function norma
    • Non-renal loss (sweat, respiratory, stool)
    • Renal loss (osmotic diuresis – glycosuria, mannitol, urea
  • Dilute urine (urine osmolarity < 250 mosm/kg)
    • Central DI
    • Renal insensitivity to ADH
      • Nephrogenic (Li or demeclocycline) DI
      • Relief of urinary tract obstruction
      • Nephritis

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